<!DOCTYPE html>
<html>
  <head>
    <title>计算器</title>
     <meta charset="utf-8">
     <meta  name="viewport" content="width=device-width" /> 
  </head>
   
<body>
<input id="num1" /> * <input id="num2" />
<button onclick="jisuan()">=</button> <input id="num3" />
 <script>
  function jisuan(){
    num3.value=num1.value*num2.value;
  }
 </script>
</body>
</html>